The Neuroprotective Ability of Polyethylene Glycol is Affected by Temperature in Ex Vivo Spinal Cord Injury Model

The cellular response to plasma membrane disruption for nanomaterial delivery

Delivery of nanomaterials into cells is of interest for fundamental cell biological research as well as for therapeutic and diagnostic purposes. One way of doing so is by physically disrupting the plasma membrane (PM). Several methods that exploit electrical, mechanical or optical cues have been conceived to temporarily disrupt the PM for intracellular delivery, with variable effects on cell viability. However, apart from acute cytotoxicity, subtler effects on cell physiology may occur as well. Their nature and timing vary with the severity of the insult and the efficiency of repair, but some may provoke permanent phenotypic alterations. With the growing palette of nanoscale delivery methods and applications, comes a need for an in-depth understanding of this cellular response. In this review, we summarize current knowledge about the chronology of cellular events that take place upon PM injury inflicted by different delivery methods. We also elaborate on their significance for cell homeostasis and cell fate. Based on the crucial nodes that govern cell fitness and functionality, we give directions for fine-tuning nano-delivery conditions.

Effects of free radical initiators on polyethylene glycol dimethacrylate hydrogel properties and biocompatibility

Many studies have utilized Irgacure 2959 photopolymerized poly(ethylene glycol) (PEG) hydrogels for tissue engineering application development. Due to the limited penetration of ultraviolet light through tissue, Irgacure 2959 polymerized hydrogels are not suitable for use in tissues where material injection is desirable, such as the spinal cord. To address this, several free radical initiators (thermal initiator VA044, ammonium persulfate (APS)/TEMED reduction-oxidation reaction, and Fenton chemistry) are evaluated for their effects on the material and mechanical properties of PEG hydrogels compared with Irgacure 2959. To emulate the effects of endogenous thiols on in vivo polymerization, the effects of chain transfer agent (CTA) dithiothreitol on gelation rates, material properties, Young's and shear modulus, are examined. Mouse embryonic stem cells and human induced pluripotent stem cell derived neural stem cells were used to investigate the cytocompatibility of each polymerization. VA044 and Fenton chemistry polymerization of PEG hydrogels both had gelation rates and mechanical properties that were highly susceptible to changes in CTA concentration and showed poor cytocompatibility. APS/TEMED polymerized hydrogels maintained consistent gelation rates and mechanical properties at high CTA concentration and had a similar cytocompatibility as Irgacure 2959 when cells were encapsulated within the PEG hydrogels. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3059-3068, 2017.

Fusogen-assisted rapid reconstitution of anatomophysiologic continuity of the transected spinal cord

The GEMINI spinal cord fusion protocol exploits the ability of so-called fusogens, such as polyethylene glycol (PEG), to achieve rapid neural restoration of electrical continuity across the ends of a transected spinal cord. Experimental evidence suggests that motor recovery can occur after complete transection of the cervical and dorsal spinal cord in mice and rats following application of PEG. This allows for the possibility of spinal cord "reconstruction" in humans and even the possibility of head transplantation in the future.

Injury potentials of spinal cord in ex vivo compression injury model

The effect of applied electric field on neuroprotection and axonal regeneration has been studied in previous studies of acute spinal cord injury (SCI). However, due to the complexity of the microenvironment of the lesion site, the underlying mechanism of applied electric field is not yet fully understood. Thus, the injury potential, a significant index of the microenvironment change, was investigated in ex vivo spinal cords compression injury. Spinal cords isolated from rat were cultured in a double sucrose gap recording chamber. Both compound action potential (CAP) and injury potential were measured. Compression induced the decreasement of compound action potential, but the amplitude of CAP increased gradually after decompression. Compression also lead to the appearance of injury potential, represented by the voltage difference between the gap potential before and after compression, and the injury potential decreased with time logarithmicly after decompression. Intracellular Na(+) and Ca(2+) concentrations were measured and results showed that after injury these ions flowed into intracellular space. Therefore, the current approach can provide a basis for investigating the formation mechanism of the injury potential and help understand the pathophysiology of the SCI.

Interaction of polyethylene glycol (PEG) with the membrane-binding domains following spinal cord injury (SCI): introduction of a mechanism for SCI repair

Lipid-binding domains regulate positioning of the membrane proteins via specific interactions with phospholipid's head groups. Spinal cord injury (SCI) diminishes the integrity of neural fiber membranes at nanoscopic level. In cases that the ruptured zone size is beyond the natural resealing ability, there is a need for reinforcing factors such as polymers (e.g. Polyethylene glycol) to patch the dismantled axoplasm. Certain conserved sequential and structural patterns of interacting residues specifically bind to PEGs. It is also found that PEG600, PEG400 and PEG200 share the strongest interaction with the lipid-binding domains even more successful than phospholipid head groups. The alpha helix structure composed of hydrophobic, neutral and acidic residues prepares an opportunity for PEG400 to play an amphipathic role in the interaction with injured membrane. This in-silico study introduces a mechanism for PEG restorative ability at the molecular level. It is believed that PEG400 interrelates the injured membrane to their underneath axoplasm while retaining the integrity of ruptured membrane via interaction with ENTH domains of membrane proteins. This privilege of PEG400 in treating injured membrane must be considered in designing of polymeric biomaterials that are introduced for SCI repair.

Efficient repairing effect of PEG based tri-block copolymer on mechanically damaged PC12 cells and isolated spinal cord

Membrane sealing effects of polymersomes made of tri-block copolymer, PEG-co-FA/SC-co-PEG, (PFSP) were studied on isolated spinal cord strips, PC12 cell lines and artificial bilayer following mechanical impact implemented by aneurism clip, sonication and electric shock, respectively. The homogeneity and size of PFSP, membrane permeability and cell viability were assessed by dynamic light scattering, LDH release and MTT assays. According to the results, the biocompatible, physico-chemical, size, surface charge and amphipathic nature of PFSP polymersome makes it an ideal macromolecule to rapidly reseal damaged membranes of cells in injured spinal cord as well as in culture medium. Compound action potentials recorded from intentionally damaged spinal cord strips incubated with PFSP showed restoration of neural excitability by 82.24 % and conduction velocity by 96.72 % after 5 min that monitored in real time. Thus, they triggered efficient instant and sustained sealing of membrane and reactivation of temporarily inactivated axons. Treatment of ultrasonically damaged PC12 cells by PFSP caused efficient cell membrane repair and led to their increased viability. The optimum effects of PFSP on stabilization and impermeabilizing of the lipid bilayer occurred at the same concentrations applied to the damaged cells and spinal cord fibers and was approved by restoration of membrane conductance and calcein release manifested by NanoDrop technique. The unique physico-chemical characteristics of novel polymersomes introduced here, make them capable to reorganize membrane lipid molecules, reseal the breaches and restore the hydrophobic insulation in spinal cord damaged cells. Thus, they might be considered in the clinical treatment of SCI at early stages.